| With the rapid development of microelectronic package and integration technology in recent years, the miniaturization of electronic components is accelerated greatly with high performance and efficiency. The low heat dissipation speed in small electronic components will shorten the service life of equipment. Polymer materials show wide application in many fields except thermal devices because of their low thermal conductivity. How to prepare the high thermal conductive polymer composites with excellent properties has attracted many concerns. In this paper, high-density polyethylene (HDPE) was used as a matrix filled with hybrid carbon materials, compound carbon materials and hybrid carbon materials/silicon carbide (SiC), respectively, to prepare thermally conductive polymer composites. The main points were summarized as follows:Firstly, we carried out carbon nanotubes (CNTs) grafting to graphene nanoplatelets (GNPs) with a silane coupling agent. The interface structure of GNPs-CNTs hybrid materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermal gravity analysis (TGA), scanning electron microscope (SEM) and Transmission electron microscopy (TEM). The results showed that CNTs and GNPs were connected to silane coupling agent through the amide group and ester group. Carbon nanotubes were successfully grafted to graphene nanoplatelets.Using GNPs-CNTs hybrid materials and GNPs/CNTs compound materials as thermally conductive filler, the effect of different filler systems on the properties of GNPs/CNTs/HDPE composites was investigated. The results showed that hybrid filler were well dispersed in the matrix. Compound filler were easy to be agglomerated, and the melt viscosity was increased apparently. The thermal conductivity of compound filler systems was higher than that of hybrid filler systems, wheares the volume resistivity was contrary. When the GNPs/CNTs compound ratio was 2:1, the thermal conductivity of composites was 1.04Wm-1K-1, which was higher than other filler systems. At the same weight ratio, the thermal conductivity of composites filled with hybrid filler system was all below 1.00 Wm-1k-1. The volume resistivity of composites dropped significantly at 5% weight ratio of compound filler, while the volume resistivity of hybrid filler system was remained above 1015Ω·cm. The thermal conductive composite with GNP-CNTs hybrid materials shows amazing insulating properties. When the GNPs/CNTs hybrid ratio was 2:1, the composites exhibited the increase of the rate of crystallization and mechanical properties compared to other filler systems. What’s more, it could effectively improve the thermal conductivity of HDPE composite at 20% weight ratio.The high thermal conductivity ceramic material SiC (120 Wm-1k-1) was selected to act as the third part to fabricate thermal conductive composite, where GNPs/CNTs grafting ratio was 2:1 as thermal conductive filler. The effects of SiC contents on the properties of hybrid thermal conductive composites were studied. The results showed that the thermal conductivity of composites increased as SiC contents increased, but the volume resistivity was declined due to the charge carrier transition between the adjacent SiC particle. When the weight ratio of SiC was 50%, the thermal conductivity of composites was increased by 136% and the volume resistivity was decreased from 3.21* 108Ω·cm to 9.89×106Ω·cm. The composites exhibited increases in the rate of crystallization at 28.6% weight ratio of SiC. With the further increase of SiC contents, the semi-crystalline time of composites was prolonged. Network structure between filler particles was very strong, and the phase separation took place in the system. The impact strength and tensile strength of composites were decreased by 64.1% and 38.4%, respectively, when the weight ratio of SiC was 50%. |
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